package org.summercool.hsf.util;

import java.io.IOException;
import java.io.Serializable;
import java.util.AbstractCollection;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @Title: ConcurrentArrayListHashMap.java
 * @Package org.summercool.hsf.util
 * @Description: TODO(添加描述)
 * @author 简道
 * @date 2011-11-18 下午9:17:25
 * @version V1.0
 */
public class ConcurrentArrayListHashMap<K, V> extends AbstractMap<K, V> implements ConcurrentMap<K, V>, Serializable {
	private static final long serialVersionUID = 7249069246763182397L;

	/*
	 * The basic strategy is to subdivide the table among Segments, each of which itself is a concurrently readable hash
	 * table.
	 */

	/* ---------------- Constants -------------- */

	/**
	 * The default initial capacity for this table, used when not otherwise specified in a constructor.
	 */
	private static final int DEFAULT_INITIAL_CAPACITY = 16;

	/**
	 * The default load factor for this table, used when not otherwise specified in a constructor.
	 */
	private static final float DEFAULT_LOAD_FACTOR = 0.75f;

	/**
	 * The default concurrency level for this table, used when not otherwise specified in a constructor.
	 */
	private static final int DEFAULT_CONCURRENCY_LEVEL = 16;

	/**
	 * The maximum capacity, used if a higher value is implicitly specified by either of the constructors with
	 * arguments. MUST be a power of two <= 1<<30 to ensure that entries are indexable using ints.
	 */
	private static final int MAXIMUM_CAPACITY = 1 << 30;

	/**
	 * The maximum number of segments to allow; used to bound constructor arguments.
	 */
	private static final int MAX_SEGMENTS = 1 << 16; // slightly conservative

	/**
	 * Number of unsynchronized retries in size and containsValue methods before resorting to locking. This is used to
	 * avoid unbounded retries if tables undergo continuous modification which would make it impossible to obtain an
	 * accurate result.
	 */
	private static final int RETRIES_BEFORE_LOCK = 2;

	/* ---------------- Fields -------------- */

	/**
	 * Mask value for indexing into segments. The upper bits of a key's hash code are used to choose the segment.
	 */
	private final int segmentMask;

	/**
	 * Shift value for indexing within segments.
	 */
	private final int segmentShift;

	/**
	 * The segments, each of which is a specialized hash table
	 */
	private final Segment<K, V>[] segments;
	/**
	 * Number of updates that alter the size of the map. This is used during bulk-read methods to make sure they see a
	 * consistent snapshot: If modCounts change during a traversal of segments computing size or checking containsValue,
	 * then we might have an inconsistent view of state so (usually) must retry.
	 */
	private transient final AtomicInteger modCount = new AtomicInteger();

	private transient int arrayVersion;
	private transient Object[] array = new Object[0];
	private transient Set<K> keySet;
	private transient Set<Map.Entry<K, V>> entrySet;
	private transient Collection<V> values;

	/* ---------------- Small Utilities -------------- */

	/**
	 * Applies a supplemental hash function to a given hashCode, which defends against poor quality hash functions. This
	 * is critical because ConcurrentArrayListHashMap uses power-of-two length hash tables, that otherwise encounter
	 * collisions for hashCodes that do not differ in lower or upper bits.
	 */
	private static int hash(int h) {
		// Spread bits to regularize both segment and index locations,
		// using variant of single-word Wang/Jenkins hash.
		h += (h << 15) ^ 0xffffcd7d;
		h ^= (h >>> 10);
		h += (h << 3);
		h ^= (h >>> 6);
		h += (h << 2) + (h << 14);
		return h ^ (h >>> 16);
	}

	/**
	 * Returns the segment that should be used for key with given hash
	 * 
	 * @param hash
	 *        the hash code for the key
	 * @return the segment
	 */
	final Segment<K, V> segmentFor(int hash) {
		return segments[(hash >>> segmentShift) & segmentMask];
	}

	/* ---------------- Inner Classes -------------- */

	/**
	 * ConcurrentArrayListHashMap list entry. Note that this is never exported out as a user-visible Map.Entry.
	 * 
	 * Because the value field is volatile, not final, it is legal wrt the Java Memory Model for an unsynchronized
	 * reader to see null instead of initial value when read via a data race. Although a reordering leading to this is
	 * not likely to ever actually occur, the Segment.readValueUnderLock method is used as a backup in case a null
	 * (pre-initialized) value is ever seen in an unsynchronized access method.
	 */
	static final class HashEntry<K, V> {
		final K key;
		final int hash;
		volatile V value;
		final HashEntry<K, V> next;

		HashEntry(K key, int hash, HashEntry<K, V> next, V value) {
			this.key = key;
			this.hash = hash;
			this.next = next;
			this.value = value;
		}

		@SuppressWarnings("unchecked")
		static final <K, V> HashEntry<K, V>[] newArray(int i) {
			return new HashEntry[i];
		}
	}

	/**
	 * Segments are specialized versions of hash tables. This subclasses from ReentrantLock opportunistically, just to
	 * simplify some locking and avoid separate construction.
	 */
	static final class Segment<K, V> extends ReentrantLock implements Serializable {
		/*
		 * Segments maintain a table of entry lists that are ALWAYS kept in a consistent state, so can be read without
		 * locking. Next fields of nodes are immutable (final). All list additions are performed at the front of each
		 * bin. This makes it easy to check changes, and also fast to traverse. When nodes would otherwise be changed,
		 * new nodes are created to replace them. This works well for hash tables since the bin lists tend to be short.
		 * (The average length is less than two for the default load factor threshold.) Read operations can thus proceed
		 * without locking, but rely on selected uses of volatiles to ensure that completed write operations performed
		 * by other threads are noticed. For most purposes, the "count" field, tracking the number of elements, serves
		 * as that volatile variable ensuring visibility. This is convenient because this field needs to be read in many
		 * read operations anyway: - All (unsynchronized) read operations must first read the "count" field, and should
		 * not look at table entries if it is 0. - All (synchronized) write operations should write to the "count" field
		 * after structurally changing any bin. The operations must not take any action that could even momentarily
		 * cause a concurrent read operation to see inconsistent data. This is made easier by the nature of the read
		 * operations in Map. For example, no operation can reveal that the table has grown but the threshold has not
		 * yet been updated, so there are no atomicity requirements for this with respect to reads. As a guide, all
		 * critical volatile reads and writes to the count field are marked in code comments.
		 */

		private static final long serialVersionUID = 2249069246763182397L;

		/**
		 * The number of elements in this segment's region.
		 */
		transient volatile int count;

		/**
		 * Number of updates that alter the size of the table. This is used during bulk-read methods to make sure they
		 * see a consistent snapshot: If modCounts change during a traversal of segments computing size or checking
		 * containsValue, then we might have an inconsistent view of state so (usually) must retry.
		 */
		transient int modCount;

		/**
		 * The table is rehashed when its size exceeds this threshold. (The value of this field is always
		 * <tt>(int)(capacity * loadFactor)</tt>.)
		 */
		transient int threshold;

		/**
		 * The per-segment table.
		 */
		transient volatile HashEntry<K, V>[] table;

		/**
		 * The load factor for the hash table. Even though this value is same for all segments, it is replicated to
		 * avoid needing links to outer object.
		 * 
		 * @serial
		 */
		final float loadFactor;

		ConcurrentArrayListHashMap<K, V> map;

		Segment(ConcurrentArrayListHashMap<K, V> map, int initialCapacity, float lf) {
			this.map = map;
			loadFactor = lf;
			setTable(HashEntry.<K, V> newArray(initialCapacity));
		}

		@SuppressWarnings("unchecked")
		static final <K, V> Segment<K, V>[] newArray(int i) {
			return new Segment[i];
		}

		/**
		 * Sets table to new HashEntry array. Call only while holding lock or in constructor.
		 */
		void setTable(HashEntry<K, V>[] newTable) {
			threshold = (int) (newTable.length * loadFactor);
			table = newTable;
		}

		/**
		 * Returns properly casted first entry of bin for given hash.
		 */
		HashEntry<K, V> getFirst(int hash) {
			HashEntry<K, V>[] tab = table;
			return tab[hash & (tab.length - 1)];
		}

		/**
		 * Reads value field of an entry under lock. Called if value field ever appears to be null. This is possible
		 * only if a compiler happens to reorder a HashEntry initialization with its table assignment, which is legal
		 * under memory model but is not known to ever occur.
		 */
		V readValueUnderLock(HashEntry<K, V> e) {
			lock();
			try {
				return e.value;
			} finally {
				unlock();
			}
		}

		/* Specialized implementations of map methods */

		V get(Object key, int hash) {
			if (count != 0) { // read-volatile
				HashEntry<K, V> e = getFirst(hash);
				while (e != null) {
					if (e.hash == hash && key.equals(e.key)) {
						V v = e.value;
						if (v != null)
							return v;
						return readValueUnderLock(e); // recheck
					}
					e = e.next;
				}
			}
			return null;
		}

		boolean containsKey(Object key, int hash) {
			if (count != 0) { // read-volatile
				HashEntry<K, V> e = getFirst(hash);
				while (e != null) {
					if (e.hash == hash && key.equals(e.key))
						return true;
					e = e.next;
				}
			}
			return false;
		}

		boolean containsValue(Object value) {
			if (count != 0) { // read-volatile
				HashEntry<K, V>[] tab = table;
				int len = tab.length;
				for (int i = 0; i < len; i++) {
					for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
						V v = e.value;
						if (v == null) // recheck
							v = readValueUnderLock(e);
						if (value.equals(v))
							return true;
					}
				}
			}
			return false;
		}

		boolean replace(K key, int hash, V oldValue, V newValue) {
			lock();
			try {
				HashEntry<K, V> e = getFirst(hash);
				while (e != null && (e.hash != hash || !key.equals(e.key)))
					e = e.next;

				boolean replaced = false;
				if (e != null && oldValue.equals(e.value)) {
					replaced = true;
					e.value = newValue;
				}
				return replaced;
			} finally {
				unlock();
			}
		}

		V replace(K key, int hash, V newValue) {
			lock();
			try {
				HashEntry<K, V> e = getFirst(hash);
				while (e != null && (e.hash != hash || !key.equals(e.key)))
					e = e.next;

				V oldValue = null;
				if (e != null) {
					oldValue = e.value;
					e.value = newValue;
				}
				return oldValue;
			} finally {
				unlock();
			}
		}

		V put(K key, int hash, V value, boolean onlyIfAbsent) {
			lock();
			try {
				int c = count;
				if (c++ > threshold) // ensure capacity
					rehash();
				HashEntry<K, V>[] tab = table;
				int index = hash & (tab.length - 1);
				HashEntry<K, V> first = tab[index];
				HashEntry<K, V> e = first;
				while (e != null && (e.hash != hash || !key.equals(e.key)))
					e = e.next;

				V oldValue;
				if (e != null) {
					oldValue = e.value;
					if (!onlyIfAbsent)
						e.value = value;
				} else {
					oldValue = null;
					++modCount;
					map.modCount.incrementAndGet();
					tab[index] = new HashEntry<K, V>(key, hash, first, value);
					count = c; // write-volatile
				}
				return oldValue;
			} finally {
				unlock();
			}
		}

		void rehash() {
			HashEntry<K, V>[] oldTable = table;
			int oldCapacity = oldTable.length;
			if (oldCapacity >= MAXIMUM_CAPACITY)
				return;

			/*
			 * Reclassify nodes in each list to new Map. Because we are using power-of-two expansion, the elements from
			 * each bin must either stay at same index, or move with a power of two offset. We eliminate unnecessary
			 * node creation by catching cases where old nodes can be reused because their next fields won't change.
			 * Statistically, at the default threshold, only about one-sixth of them need cloning when a table doubles.
			 * The nodes they replace will be garbage collectable as soon as they are no longer referenced by any reader
			 * thread that may be in the midst of traversing table right now.
			 */

			HashEntry<K, V>[] newTable = HashEntry.newArray(oldCapacity << 1);
			threshold = (int) (newTable.length * loadFactor);
			int sizeMask = newTable.length - 1;
			for (int i = 0; i < oldCapacity; i++) {
				// We need to guarantee that any existing reads of old Map can
				// proceed. So we cannot yet null out each bin.
				HashEntry<K, V> e = oldTable[i];

				if (e != null) {
					HashEntry<K, V> next = e.next;
					int idx = e.hash & sizeMask;

					// Single node on list
					if (next == null)
						newTable[idx] = e;

					else {
						// Reuse trailing consecutive sequence at same slot
						HashEntry<K, V> lastRun = e;
						int lastIdx = idx;
						for (HashEntry<K, V> last = next; last != null; last = last.next) {
							int k = last.hash & sizeMask;
							if (k != lastIdx) {
								lastIdx = k;
								lastRun = last;
							}
						}
						newTable[lastIdx] = lastRun;

						// Clone all remaining nodes
						for (HashEntry<K, V> p = e; p != lastRun; p = p.next) {
							int k = p.hash & sizeMask;
							HashEntry<K, V> n = newTable[k];
							newTable[k] = new HashEntry<K, V>(p.key, p.hash, n, p.value);
						}
					}
				}
			}
			table = newTable;
		}

		/**
		 * Remove; match on key only if value null, else match both.
		 */
		V remove(Object key, int hash, Object value) {
			lock();
			try {
				int c = count - 1;
				HashEntry<K, V>[] tab = table;
				int index = hash & (tab.length - 1);
				HashEntry<K, V> first = tab[index];
				HashEntry<K, V> e = first;
				while (e != null && (e.hash != hash || !key.equals(e.key)))
					e = e.next;

				V oldValue = null;
				if (e != null) {
					V v = e.value;
					if (value == null || value.equals(v)) {
						oldValue = v;
						// All entries following removed node can stay
						// in list, but all preceding ones need to be
						// cloned.
						++modCount;
						map.modCount.incrementAndGet();
						HashEntry<K, V> newFirst = e.next;
						for (HashEntry<K, V> p = first; p != e; p = p.next)
							newFirst = new HashEntry<K, V>(p.key, p.hash, newFirst, p.value);
						tab[index] = newFirst;
						count = c; // write-volatile
					}
				}
				return oldValue;
			} finally {
				unlock();
			}
		}

		void clear() {
			if (count != 0) {
				lock();
				try {
					HashEntry<K, V>[] tab = table;
					for (int i = 0; i < tab.length; i++)
						tab[i] = null;
					++modCount;
					map.modCount.incrementAndGet();
					count = 0; // write-volatile
				} finally {
					unlock();
				}
			}
		}
	}

	/* ---------------- Public operations -------------- */

	/**
	 * Creates a new, empty map with the specified initial capacity, load factor and concurrency level.
	 * 
	 * @param initialCapacity
	 *        the initial capacity. The implementation performs internal sizing to accommodate this many elements.
	 * @param loadFactor
	 *        the load factor threshold, used to control resizing. Resizing may be performed when the average number of
	 *        elements per bin exceeds this threshold.
	 * @param concurrencyLevel
	 *        the estimated number of concurrently updating threads. The implementation performs internal sizing to try
	 *        to accommodate this many threads.
	 * @throws IllegalArgumentException
	 *         if the initial capacity is negative or the load factor or concurrencyLevel are nonpositive.
	 */
	public ConcurrentArrayListHashMap(int initialCapacity, float loadFactor, int concurrencyLevel) {
		if (!(loadFactor > 0) || initialCapacity < 0 || concurrencyLevel <= 0)
			throw new IllegalArgumentException();

		if (concurrencyLevel > MAX_SEGMENTS)
			concurrencyLevel = MAX_SEGMENTS;

		// Find power-of-two sizes best matching arguments
		int sshift = 0;
		int ssize = 1;
		while (ssize < concurrencyLevel) {
			++sshift;
			ssize <<= 1;
		}
		segmentShift = 32 - sshift;
		segmentMask = ssize - 1;
		this.segments = Segment.newArray(ssize);

		if (initialCapacity > MAXIMUM_CAPACITY)
			initialCapacity = MAXIMUM_CAPACITY;
		int c = initialCapacity / ssize;
		if (c * ssize < initialCapacity)
			++c;
		int cap = 1;
		while (cap < c)
			cap <<= 1;

		for (int i = 0; i < this.segments.length; ++i)
			this.segments[i] = new Segment<K, V>(this, cap, loadFactor);
	}

	/**
	 * Creates a new, empty map with the specified initial capacity and load factor and with the default
	 * concurrencyLevel (16).
	 * 
	 * @param initialCapacity
	 *        The implementation performs internal sizing to accommodate this many elements.
	 * @param loadFactor
	 *        the load factor threshold, used to control resizing. Resizing may be performed when the average number of
	 *        elements per bin exceeds this threshold.
	 * @throws IllegalArgumentException
	 *         if the initial capacity of elements is negative or the load factor is nonpositive
	 * 
	 * @since 1.6
	 */
	public ConcurrentArrayListHashMap(int initialCapacity, float loadFactor) {
		this(initialCapacity, loadFactor, DEFAULT_CONCURRENCY_LEVEL);
	}

	/**
	 * Creates a new, empty map with the specified initial capacity, and with default load factor (0.75) and
	 * concurrencyLevel (16).
	 * 
	 * @param initialCapacity
	 *        the initial capacity. The implementation performs internal sizing to accommodate this many elements.
	 * @throws IllegalArgumentException
	 *         if the initial capacity of elements is negative.
	 */
	public ConcurrentArrayListHashMap(int initialCapacity) {
		this(initialCapacity, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
	}

	/**
	 * Creates a new, empty map with a default initial capacity (16), load factor (0.75) and concurrencyLevel (16).
	 */
	public ConcurrentArrayListHashMap() {
		this(DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR, DEFAULT_CONCURRENCY_LEVEL);
	}

	/**
	 * Creates a new map with the same mappings as the given map. The map is created with a capacity of 1.5 times the
	 * number of mappings in the given map or 16 (whichever is greater), and a default load factor (0.75) and
	 * concurrencyLevel (16).
	 * 
	 * @param m
	 *        the map
	 */
	public ConcurrentArrayListHashMap(Map<? extends K, ? extends V> m) {
		this(Math.max((int) (m.size() / DEFAULT_LOAD_FACTOR) + 1, DEFAULT_INITIAL_CAPACITY), DEFAULT_LOAD_FACTOR,
				DEFAULT_CONCURRENCY_LEVEL);
		putAll(m);
	}

	/**
	 * Returns <tt>true</tt> if this map contains no key-value mappings.
	 * 
	 * @return <tt>true</tt> if this map contains no key-value mappings
	 */
	public boolean isEmpty() {
		final Segment<K, V>[] segments = this.segments;
		/*
		 * We keep track of per-segment modCounts to avoid ABA problems in which an element in one segment was added and
		 * in another removed during traversal, in which case the table was never actually empty at any point. Note the
		 * similar use of modCounts in the size() and containsValue() methods, which are the only other methods also
		 * susceptible to ABA problems.
		 */
		int[] mc = new int[segments.length];
		int mcsum = 0;
		for (int i = 0; i < segments.length; ++i) {
			if (segments[i].count != 0)
				return false;
			else
				mcsum += mc[i] = segments[i].modCount;
		}
		// If mcsum happens to be zero, then we know we got a snapshot
		// before any modifications at all were made. This is
		// probably common enough to bother tracking.
		if (mcsum != 0) {
			for (int i = 0; i < segments.length; ++i) {
				if (segments[i].count != 0 || mc[i] != segments[i].modCount)
					return false;
			}
		}
		return true;
	}

	/**
	 * Returns the number of key-value mappings in this map. If the map contains more than <tt>Integer.MAX_VALUE</tt>
	 * elements, returns <tt>Integer.MAX_VALUE</tt>.
	 * 
	 * @return the number of key-value mappings in this map
	 */
	public int size() {
		final Segment<K, V>[] segments = this.segments;
		long sum = 0;
		long check = 0;
		int[] mc = new int[segments.length];
		// Try a few times to get accurate count. On failure due to
		// continuous async changes in table, resort to locking.
		for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
			check = 0;
			sum = 0;
			int mcsum = 0;
			for (int i = 0; i < segments.length; ++i) {
				sum += segments[i].count;
				mcsum += mc[i] = segments[i].modCount;
			}
			if (mcsum != 0) {
				for (int i = 0; i < segments.length; ++i) {
					check += segments[i].count;
					if (mc[i] != segments[i].modCount) {
						check = -1; // force retry
						break;
					}
				}
			}
			if (check == sum)
				break;
		}
		if (check != sum) { // Resort to locking all segments
			sum = 0;
			for (int i = 0; i < segments.length; ++i)
				segments[i].lock();
			for (int i = 0; i < segments.length; ++i)
				sum += segments[i].count;
			for (int i = 0; i < segments.length; ++i)
				segments[i].unlock();
		}
		if (sum > Integer.MAX_VALUE)
			return Integer.MAX_VALUE;
		else
			return (int) sum;
	}

	/**
	 * Returns the value to which the specified key is mapped, or {@code null} if this map contains no mapping for the
	 * key.
	 * 
	 * <p> More formally, if this map contains a mapping from a key {@code k} to a value {@code v} such that
	 * {@code key.equals(k)}, then this method returns {@code v}; otherwise it returns {@code null}. (There can be at
	 * most one such mapping.)
	 * 
	 * @throws NullPointerException
	 *         if the specified key is null
	 */
	public V get(Object key) {
		int hash = hash(key.hashCode());
		return segmentFor(hash).get(key, hash);
	}

	/**
	 * Tests if the specified object is a key in this table.
	 * 
	 * @param key
	 *        possible key
	 * @return <tt>true</tt> if and only if the specified object is a key in this table, as determined by the
	 *         <tt>equals</tt> method; <tt>false</tt> otherwise.
	 * @throws NullPointerException
	 *         if the specified key is null
	 */
	public boolean containsKey(Object key) {
		int hash = hash(key.hashCode());
		return segmentFor(hash).containsKey(key, hash);
	}

	/**
	 * Returns <tt>true</tt> if this map maps one or more keys to the specified value. Note: This method requires a full
	 * internal traversal of the hash table, and so is much slower than method <tt>containsKey</tt>.
	 * 
	 * @param value
	 *        value whose presence in this map is to be tested
	 * @return <tt>true</tt> if this map maps one or more keys to the specified value
	 * @throws NullPointerException
	 *         if the specified value is null
	 */
	public boolean containsValue(Object value) {
		if (value == null)
			throw new NullPointerException();

		// See explanation of modCount use above

		final Segment<K, V>[] segments = this.segments;
		int[] mc = new int[segments.length];

		// Try a few times without locking
		for (int k = 0; k < RETRIES_BEFORE_LOCK; ++k) {
			// unused
			// int sum = 0;
			int mcsum = 0;
			for (int i = 0; i < segments.length; ++i) {
				// unused
				// int c = segments[i].count;
				mcsum += mc[i] = segments[i].modCount;
				if (segments[i].containsValue(value))
					return true;
			}
			boolean cleanSweep = true;
			if (mcsum != 0) {
				for (int i = 0; i < segments.length; ++i) {
					// unused
					// int c = segments[i].count;
					if (mc[i] != segments[i].modCount) {
						cleanSweep = false;
						break;
					}
				}
			}
			if (cleanSweep)
				return false;
		}
		// Resort to locking all segments
		for (int i = 0; i < segments.length; ++i)
			segments[i].lock();
		boolean found = false;
		try {
			for (int i = 0; i < segments.length; ++i) {
				if (segments[i].containsValue(value)) {
					found = true;
					break;
				}
			}
		} finally {
			for (int i = 0; i < segments.length; ++i)
				segments[i].unlock();
		}
		return found;
	}

	/**
	 * Legacy method testing if some key maps into the specified value in this table. This method is identical in
	 * functionality to {@link #containsValue}, and exists solely to ensure full compatibility with class
	 * {@link java.util.Hashtable}, which supported this method prior to introduction of the Java Collections framework.
	 * 
	 * @param value
	 *        a value to search for
	 * @return <tt>true</tt> if and only if some key maps to the <tt>value</tt> argument in this table as determined by
	 *         the <tt>equals</tt> method; <tt>false</tt> otherwise
	 * @throws NullPointerException
	 *         if the specified value is null
	 */
	public boolean contains(Object value) {
		return containsValue(value);
	}

	/**
	 * Maps the specified key to the specified value in this table. Neither the key nor the value can be null.
	 * 
	 * <p> The value can be retrieved by calling the <tt>get</tt> method with a key that is equal to the original key.
	 * 
	 * @param key
	 *        key with which the specified value is to be associated
	 * @param value
	 *        value to be associated with the specified key
	 * @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no mapping for
	 *         <tt>key</tt>
	 * @throws NullPointerException
	 *         if the specified key or value is null
	 */
	public V put(K key, V value) {
		if (value == null)
			throw new NullPointerException();
		int hash = hash(key.hashCode());
		return segmentFor(hash).put(key, hash, value, false);
	}

	/**
	 * {@inheritDoc}
	 * 
	 * @return the previous value associated with the specified key, or <tt>null</tt> if there was no mapping for the
	 *         key
	 * @throws NullPointerException
	 *         if the specified key or value is null
	 */
	public V putIfAbsent(K key, V value) {
		if (value == null)
			throw new NullPointerException();
		int hash = hash(key.hashCode());
		return segmentFor(hash).put(key, hash, value, true);
	}

	/**
	 * Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map
	 * had for any of the keys currently in the specified map.
	 * 
	 * @param m
	 *        mappings to be stored in this map
	 */
	public void putAll(Map<? extends K, ? extends V> m) {
		for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
			put(e.getKey(), e.getValue());
	}

	/**
	 * Removes the key (and its corresponding value) from this map. This method does nothing if the key is not in the
	 * map.
	 * 
	 * @param key
	 *        the key that needs to be removed
	 * @return the previous value associated with <tt>key</tt>, or <tt>null</tt> if there was no mapping for
	 *         <tt>key</tt>
	 * @throws NullPointerException
	 *         if the specified key is null
	 */
	public V remove(Object key) {
		int hash = hash(key.hashCode());
		return segmentFor(hash).remove(key, hash, null);
	}

	/**
	 * {@inheritDoc}
	 * 
	 * @throws NullPointerException
	 *         if the specified key is null
	 */
	public boolean remove(Object key, Object value) {
		int hash = hash(key.hashCode());
		if (value == null)
			return false;
		return segmentFor(hash).remove(key, hash, value) != null;
	}

	/**
	 * {@inheritDoc}
	 * 
	 * @throws NullPointerException
	 *         if any of the arguments are null
	 */
	public boolean replace(K key, V oldValue, V newValue) {
		if (oldValue == null || newValue == null)
			throw new NullPointerException();
		int hash = hash(key.hashCode());
		return segmentFor(hash).replace(key, hash, oldValue, newValue);
	}

	/**
	 * {@inheritDoc}
	 * 
	 * @return the previous value associated with the specified key, or <tt>null</tt> if there was no mapping for the
	 *         key
	 * @throws NullPointerException
	 *         if the specified key or value is null
	 */
	public V replace(K key, V value) {
		if (value == null)
			throw new NullPointerException();
		int hash = hash(key.hashCode());
		return segmentFor(hash).replace(key, hash, value);
	}

	/**
	 * Removes all of the mappings from this map.
	 */
	public void clear() {
		for (int i = 0; i < segments.length; ++i)
			segments[i].clear();
	}

	/**
	 * Returns a {@link Set} view of the keys contained in this map. The set is backed by the map, so changes to the map
	 * are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding
	 * mapping from this map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
	 * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
	 * operations.
	 * 
	 * <p> The view's <tt>iterator</tt> is a "weakly consistent" iterator that will never throw
	 * {@link ConcurrentModificationException}, and guarantees to traverse elements as they existed upon construction of
	 * the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.
	 */
	public Set<K> keySet() {
		Set<K> ks = keySet;
		return (ks != null) ? ks : (keySet = new KeySet());
	}

	/**
	 * Returns a {@link Collection} view of the values contained in this map. The collection is backed by the map, so
	 * changes to the map are reflected in the collection, and vice-versa. The collection supports element removal,
	 * which removes the corresponding mapping from this map, via the <tt>Iterator.remove</tt>,
	 * <tt>Collection.remove</tt>, <tt>removeAll</tt>, <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not
	 * support the <tt>add</tt> or <tt>addAll</tt> operations.
	 * 
	 * <p> The view's <tt>iterator</tt> is a "weakly consistent" iterator that will never throw
	 * {@link ConcurrentModificationException}, and guarantees to traverse elements as they existed upon construction of
	 * the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.
	 */
	public Collection<V> values() {
		Collection<V> vs = values;
		return (vs != null) ? vs : (values = new Values());
	}

	public Object[] arrayValues() {
		if (arrayVersion == modCount.get()) {
			return array;
		} else {
			Collection<V> vs = values();
			array = vs.toArray();
			arrayVersion = modCount.get();
			return array;
		}
	}

	/**
	 * Returns a {@link Set} view of the mappings contained in this map. The set is backed by the map, so changes to the
	 * map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding
	 * mapping from the map, via the <tt>Iterator.remove</tt>, <tt>Set.remove</tt>, <tt>removeAll</tt>,
	 * <tt>retainAll</tt>, and <tt>clear</tt> operations. It does not support the <tt>add</tt> or <tt>addAll</tt>
	 * operations.
	 * 
	 * <p> The view's <tt>iterator</tt> is a "weakly consistent" iterator that will never throw
	 * {@link ConcurrentModificationException}, and guarantees to traverse elements as they existed upon construction of
	 * the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.
	 */
	public Set<Map.Entry<K, V>> entrySet() {
		Set<Map.Entry<K, V>> es = entrySet;
		return (es != null) ? es : (entrySet = new EntrySet());
	}

	/**
	 * Returns an enumeration of the keys in this table.
	 * 
	 * @return an enumeration of the keys in this table
	 * @see #keySet()
	 */
	public Enumeration<K> keys() {
		return new KeyIterator();
	}

	/**
	 * Returns an enumeration of the values in this table.
	 * 
	 * @return an enumeration of the values in this table
	 * @see #values()
	 */
	public Enumeration<V> elements() {
		return new ValueIterator();
	}

	/* ---------------- Iterator Support -------------- */

	abstract class HashIterator {
		int nextSegmentIndex;
		int nextTableIndex;
		HashEntry<K, V>[] currentTable;
		HashEntry<K, V> nextEntry;
		HashEntry<K, V> lastReturned;

		HashIterator() {
			nextSegmentIndex = segments.length - 1;
			nextTableIndex = -1;
			advance();
		}

		public boolean hasMoreElements() {
			return hasNext();
		}

		final void advance() {
			if (nextEntry != null && (nextEntry = nextEntry.next) != null)
				return;

			while (nextTableIndex >= 0) {
				if ((nextEntry = currentTable[nextTableIndex--]) != null)
					return;
			}

			while (nextSegmentIndex >= 0) {
				Segment<K, V> seg = segments[nextSegmentIndex--];
				if (seg.count != 0) {
					currentTable = seg.table;
					for (int j = currentTable.length - 1; j >= 0; --j) {
						if ((nextEntry = currentTable[j]) != null) {
							nextTableIndex = j - 1;
							return;
						}
					}
				}
			}
		}

		public boolean hasNext() {
			return nextEntry != null;
		}

		HashEntry<K, V> nextEntry() {
			if (nextEntry == null)
				throw new NoSuchElementException();
			lastReturned = nextEntry;
			advance();
			return lastReturned;
		}

		public void remove() {
			if (lastReturned == null)
				throw new IllegalStateException();
			ConcurrentArrayListHashMap.this.remove(lastReturned.key);
			lastReturned = null;
		}
	}

	final class KeyIterator extends HashIterator implements Iterator<K>, Enumeration<K> {
		public K next() {
			return super.nextEntry().key;
		}

		public K nextElement() {
			return super.nextEntry().key;
		}
	}

	final class ValueIterator extends HashIterator implements Iterator<V>, Enumeration<V> {
		public V next() {
			return super.nextEntry().value;
		}

		public V nextElement() {
			return super.nextEntry().value;
		}
	}

	/**
	 * Custom Entry class used by EntryIterator.next(), that relays setValue changes to the underlying map.
	 */
	@SuppressWarnings("serial")
	final class WriteThroughEntry extends AbstractMap.SimpleEntry<K, V> {
		WriteThroughEntry(K k, V v) {
			super(k, v);
		}

		/**
		 * Set our entry's value and write through to the map. The value to return is somewhat arbitrary here. Since a
		 * WriteThroughEntry does not necessarily track asynchronous changes, the most recent "previous" value could be
		 * different from what we return (or could even have been removed in which case the put will re-establish). We
		 * do not and cannot guarantee more.
		 */
		public V setValue(V value) {
			if (value == null)
				throw new NullPointerException();
			V v = super.setValue(value);
			ConcurrentArrayListHashMap.this.put(getKey(), value);
			return v;
		}
	}

	final class EntryIterator extends HashIterator implements Iterator<Entry<K, V>> {
		public Map.Entry<K, V> next() {
			HashEntry<K, V> e = super.nextEntry();
			return new WriteThroughEntry(e.key, e.value);
		}
	}

	final class KeySet extends AbstractSet<K> {
		public Iterator<K> iterator() {
			return new KeyIterator();
		}

		public int size() {
			return ConcurrentArrayListHashMap.this.size();
		}

		public boolean contains(Object o) {
			return ConcurrentArrayListHashMap.this.containsKey(o);
		}

		public boolean remove(Object o) {
			return ConcurrentArrayListHashMap.this.remove(o) != null;
		}

		public void clear() {
			ConcurrentArrayListHashMap.this.clear();
		}
	}

	final class Values extends AbstractCollection<V> {
		public Iterator<V> iterator() {
			return new ValueIterator();
		}

		public int size() {
			return ConcurrentArrayListHashMap.this.size();
		}

		public boolean contains(Object o) {
			return ConcurrentArrayListHashMap.this.containsValue(o);
		}

		public void clear() {
			ConcurrentArrayListHashMap.this.clear();
		}
	}

	final class EntrySet extends AbstractSet<Map.Entry<K, V>> {
		public Iterator<Map.Entry<K, V>> iterator() {
			return new EntryIterator();
		}

		public boolean contains(Object o) {
			if (!(o instanceof Map.Entry))
				return false;
			Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
			V v = ConcurrentArrayListHashMap.this.get(e.getKey());
			return v != null && v.equals(e.getValue());
		}

		public boolean remove(Object o) {
			if (!(o instanceof Map.Entry))
				return false;
			Map.Entry<?, ?> e = (Map.Entry<?, ?>) o;
			return ConcurrentArrayListHashMap.this.remove(e.getKey(), e.getValue());
		}

		public int size() {
			return ConcurrentArrayListHashMap.this.size();
		}

		public void clear() {
			ConcurrentArrayListHashMap.this.clear();
		}
	}

	/* ---------------- Serialization Support -------------- */

	/**
	 * Save the state of the <tt>ConcurrentArrayListHashMap</tt> instance to a stream (i.e., serialize it).
	 * 
	 * @param s
	 *        the stream
	 * @serialData the key (Object) and value (Object) for each key-value mapping, followed by a null pair. The
	 *             key-value mappings are emitted in no particular order.
	 */
	private void writeObject(java.io.ObjectOutputStream s) throws IOException {
		s.defaultWriteObject();

		for (int k = 0; k < segments.length; ++k) {
			Segment<K, V> seg = segments[k];
			seg.lock();
			try {
				HashEntry<K, V>[] tab = seg.table;
				for (int i = 0; i < tab.length; ++i) {
					for (HashEntry<K, V> e = tab[i]; e != null; e = e.next) {
						s.writeObject(e.key);
						s.writeObject(e.value);
					}
				}
			} finally {
				seg.unlock();
			}
		}
		s.writeObject(null);
		s.writeObject(null);
	}

	/**
	 * Reconstitute the <tt>ConcurrentArrayListHashMap</tt> instance from a stream (i.e., deserialize it).
	 * 
	 * @param s
	 *        the stream
	 */
	@SuppressWarnings("unchecked")
	private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException {
		s.defaultReadObject();

		// Initialize each segment to be minimally sized, and let grow.
		for (int i = 0; i < segments.length; ++i) {
			segments[i].setTable(new HashEntry[1]);
		}

		// Read the keys and values, and put the mappings in the table
		for (;;) {
			K key = (K) s.readObject();
			V value = (V) s.readObject();
			if (key == null)
				break;
			put(key, value);
		}
	}
}
